This invention relates to a valve generally used to control a vacuum-motor in response to a vacuum signal from a monitored source. More specifically this invention relates to control of a vacuum-operated idle speed control system to provide a timed delay function for only an incremental portion of the total vacuum level change.
Delay valves are in widespread use through the automotive industry for control functions. In the present case a delay valve in a vacuum line may be connected, through a controlling dashpot, to the idle control of an automobile engine. The dashpot generally controls carburetor throttle opening in response to a signal from the delay valve, which valve is responsive to a vacuum signal, such as the manifold vacuum. A delay valve has a time delay between the sensing of a vacuum level change and responding or "delivering the message" of a vacuum level change to the controlled element or device.
In the case of an automobile the failure of the dashpot to quickly respond to a rapid reduction in the manifold vacuum due to a delay valve leads to a more widely open throttle, causing higher engine revolutions per minute (rpm) and consequently higher gas consumption. Present valve arrangements prevent the idle speed dashpot from overcompensating for suddenly changing engine conditions through relatively long time delays between an engine rpm change and a response change in the dashpot based upon the engine change.
A singular method of controlling a segment of engine rpm change would be to avoid the use of a delay valve, but this would lead to erratic engine operating conditions and pollution control problems. Alternatively, a controlled bypass of a delay valve, under a given condition or after a fixed parameter is exceeded, would be preferred. Such a bypass arrangement would still allow the delay valve to operate in its present mode of allowing delay times for gradual engine changing conditions, and nevertheless overcome that condition where there is a rapid change in the monitored condition, such as a rapid decrease in engine manifold vacuum (i.e., an increase in pressure level).